Duck stores protein regularly in type of feather (7)

I believe the answer is:

tertial

I'm a little stuck... Click here to teach me more about this clue!

'type of feather' is the definition.
'tertial' can be an answer for 'feather' (I've seen this before). I am unsure of the 'type of' bit.

'duck stores protein regularly' is the wordplay.
'duck' becomes 'teal' (teal is a kind of duck).
'stores' indicates putting letters inside.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'protein' are 'rti'.
'teal' going around 'rti' is 'TERTIAL'.

'in' is the link.

Can you help me to learn more?

(Another definition for tertial that I've seen is " feather".)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.